Intake system of a multi-cylinder internal combustion engine

ABSTRACT

A multi-cylinder engine comprising a carburetor housing forming therein at least two branch mixture passages. Each of the branch mixture passages is connected to a respective intake port. A throttle valve of the carburetor is provided for each cylinder. Each of the throttle valves is arranged in the respective branch mixture passage and attached onto a common throttle shaft. A wedge shaped groove is formed on the upper inner wall of each of the branch mixture passages, and the common throttle shaft is arranged in the wedge shaped groove for causing the mixture to flow only along the bottom wall of the branch mixture passage. A single common connecting passage and branch connecting passages which are connected to the common connecting passage are provided. Each of the branch connecting passages opens into the respective intake port in the vicinity of the rear face of the valve head of the corresponding intake valve.

DESCRIPTION OF THE INVENTION

The present invention relates to an intake system of a multi-cylinderinternal combustion engine.

Particularly in a gasoline engine, in order to obtain a high outputpower of the engine by increasing the volumetric efficiency when theengine is operating at a high speed under a heavy load, the shape of anintake port is so constructed that the intake port has as small a flowresistance as possible. In the case wherein the intake port has such ashape, since a considerably strong turbulence is spontaneously createdin the combustion chamber of the engine when the engine is operating ata high speed under a heavy load, the burning velocity is sufficientlyincreased. However, when the same engine is operating at a low speed, asatisfactory strong turbulence is not created in the combustion chamber,thus resulting in a problem in that a sufficient increase in the burningvelocity is not obtained.

As a method of creating a strong turbulence in the combustion chamberwhen an engine is operating at a low speed, there is a method ofcompulsorily creating a swirl motion in the combustion chamber by usinga helically-shaped intake port or by using a shroud valve. However, inthe case wherein such a method is adopted, since the flow resistance towhich the mixture fed into the cylinder is subjected is increased, aproblem occurs in that the volumetric efficiency is reduced when anengine is operating at a high speed under a heavy load. In addition, asan engine capable of creating a strong turbulence in the combustionchamber, an engine has been proposed, in which an intake passagecomprises a main intake passage having a relatively large cross-section,and an auxiliary intake passage having a relatively small cross-sectionand opening into the intake port. In this engine, the mixture is fedinto the combustion chamber from the auxiliary intake passage via theintake port when an engine is operating under a light load; as a result,a turbulence is produced in the combustion chamber by the mixturespouted from the auxiliary intake passage at a high speed. On the otherhand, when an engine is operating under a heavy load, the mixture is fedinto the combustion chamber via the main intake passage. It is truethat, in this engine, it is possible to produce a strong turbulence inthe combustion chamber when an engine is operating at a low speed undera light load, while ensuring a high volumetric efficiency when theengine is operating at a high speed under a heavy load. However, thisengine has drawbacks in that the construction of a mixture passageswitching mechanism for switching the mixture passage from the mainintake passage to the auxiliary intake passage is complicated; inaddition, it is impossible to produce a strong turbulence in thecombustion chamber when the engine is operating at a low speed under aheavy load.

An object of the present invention is to provide an intake system of aninternal combustion engine, which has a simple construction and which iscapable of creating a strong turbulence in the combustion chamberindependently of the engine speed when an engine is operating under alight load while ensuring a high volumetric efficiency when the engineis operating at a high speed under a heavy load.

According to the present invention, there is provided a multi-cylinderinternal combustion engine having a plurality of cylinders, each havinga combustion chamber and an intake valve which has a valve head, saidengine comprising: at least one intake passage common to at least twocylinders and comprising a collecting portion having an inlet, and atleast two branch intake passages branched off from said collectingportion, each of said branch intake passages having an upper wall and abottom wall and being connected said respective combustion chamber viasaid corresponding intake valve; fuel supply means arranged in the inletof said collecting portion; a common connecting passage; at least twobranch connecting passages, each being connected to said commonconnecting passage and having an opening which opens into saidrespective branch intake passage, and; at least two rotatable throttlevalves each being arranged in said respective branch intake passage at aposition upstream of the opening of said corresponding branch connectingpassage and having an upper edge and a lower edge which cooperates withthe bottom wall of said corresponding branch intake passage to formtherebetween a mixture flow passage, the cross sectional area of whichis increased as the corresponding throttle valve is rotated inaccordance with an increase in the level of the load of said engine, theupper edge of each of said throttle valves cooperating with the upperwall of said corresponding branch intake passage to prevent a mixturefrom flowing between the upper edge of said corresponding throttle valveand the upper wall of said corresponding branch intake passage.

The present invention may be more fully understood from the descriptionof preferred embodiments of the invention set forth below, together withthe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a plan view, partly in cross-section, of an embodiment of anengine according to the present invention;

FIG. 2 is a cross-sectional side view taken along the line II--II inFIG. 1;

FIG. 3 is a cross-sectional view taken along the III--III in FIG. 2;

FIG. 4 is a plan view, partly in cross-section, of another embodimentaccording to the present invention;

FIG. 5 is a cross-sectional side view of a further embodiment accordingto the present invention;

FIG. 6 is a cross-sectional view taken along the line VI--VI in FIG. 5;

FIG. 7 is a plan view, partly in cross-section, of the engineillustrated in FIG. 5, and;

FIG. 8 is a graph showing changes in pressure in the intake port locatedat a position near the rear face of the valve head of the intake valve.

DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to FIG. 1, 1 designates an engine body; 2a, 2b, 2c, 2ddesignate No. 1 cylinder, No. 2 cylinder, No. 3 cylinder and No. 4cylinder, respectively; 3a, 3b, 3c, 3d designate intake valves; 4a, 4b,4c, 4d exhaust valves; 5a, 5b, 5c, 5d intake ports; and 6a, 6b, 6c, 6dexhaust ports. Referring to FIG. 2, reference numeral 7 designates acylinder block, 8 a piston which is reciprocally movable in the cylinderblock 7, 9 a cylinder head fixed onto the cylinder block 7, and 10 acombustion chamber. The spark plug (not shown) is arranged in thecombustion chamber 10.

Referring to FIGS. 1 and 2, a pair of carburetor housings 11, 12 ismounted on the engine body 1, and variable venturi type carburetorbodies 13, 14 are arranged in the carburetor housings 11, 12,respectively. Each of the mixture passages 15, 16 formed in thecarburetor housings 11, 12 is divided into four respective branchmixture passages 17, 18, 19, 20, and each of the branch mixture passages17, 18, 19, 20 is respectively connected to the intake ports 5a, 5b, 5c,5d. Throttle valves 21, 22, 23, 24 of the carburetor bodies 13, 14 arearranged in the corresponding branch mixture passages 17, 18, 19, 20 andattached onto a common valve shaft 25. However, instead of beingattached onto the common valve shaft 25, the throttle valves 21, 22, 23,24 may be interconnected to each other by means of a link mechanism (notshown) so that the opening operation of all the throttle valves 21, 22,23, 24 is controlled at the same time. As is illustrated in FIG. 2, awedge shaped groove 32 is formed on the upper inner wall of the branchmixture passage 18, and the throttle shaft 25 is arranged in the wedgeshaped groove 32. By positioning the throttle shaft 25 in the wedgeshaped groove 32, the flow-resistance which the mixture flowing in thebranch mixture passage 18 is subjected to becomes extremely small whenthe throttle valve 22 is fully opened, as illustrated by the broken linein FIG. 2. In addition, as is illustrated in FIG. 2, the carburetor body13 comprises a movable suction piston 26, a movable needle 27 and ametering jet 28. As is well known to those skilled in the art, thesuction piston 26 moves up and down so that the vacuum produced in themixture passage 15 located between the suction piston 26 and thethrottle valve 22 is maintained at a constant level.

A common connecting channel 29 extending in the longitudinal directionof the engine body 1 and having a cross-section which is smaller thanthat of the branch mixture passages 17, 18, 19, 20 is arranged beneaththe throttle valves 21, 22, 23, 24. In addition, four channel branches30a, 30b, 30c, 30d which are in communication with the common connectingchannel 29 and which have a cross-section smaller than that of thebranch mixture passages 17, 18, 19, 20 are formed in the cylinder head9, and the channel branches 30a, 30b, 30c, 30d open into the intakeports 5a, 5b, 5c, 5d at a position near the rear faces of the valveheads of the corresponding intake valves 3a, 3b, 3c, 3d, respectively.The openings of the channel branches 30a, 30b, 30c, 30d are directed tovalve gaps formed between the corresponding intake valves 3a, 3b, 3c, 3dand their valve seats when the intake valves 3a, 3b, 3c, 3d are opened,respectively.

FIG. 8 illustrates changes in pressure in the intake ports 5a, 5b, 5c,5d. In FIG. 8, the abscissa θ indicates a crank angle, and the ordinateP indicates pressure in the intake port in the vicinity of the rear faceof the valve head of the intake valve (hereinafter referred to as anintake port pressure). In addition, each of the reference lines A, B, C,D indicates the atmospheric pressure. Furthermore, in FIG. 8, the curvedlines E, F, G and H indicate changes in the intake port pressure in theintake ports 5a, 5b, 5c and 5d, respectively, and the arrows I, J, K andL indicate the opening duration of the intake valves 3a, 3b, 3c and 3d,respectively. Referring to the change in pressure in the No. 1 PG,9cylinder shown in FIG. 8, the intake port pressure becomes a positivepressure over the range M of the crank angle immediately after theintake valve is opened, and then a vacuum is produced in the intake portof the No. 1 cylinder over the range N of the crank angle in which thepiston moves downwards. After this, the intake port pressure againbecomes a positive pressure over the range O of the crank angle afterthe piston begins to move upwards. The change in the intake portpressure in the remaining cylinders is the same as that in the intakeport pressure in the No. 1 cylinder. Consequently, referring to therange P of the crank angle of the No. 1 cylinder and No. 2 cylindershown in FIG. 8, it will be understood that a vacuum is produced in theintake port of the No. 1 cylinder, and that, at this time, the intakeport pressure of the No. 2 cylinder is positive. In addition, from FIG.8 it will be understood that, referring to the range Q of the crankangle of the No. 2 cylinder and No. 4 cylinder, a vacuum is produced inthe intake port of the No. 2 cylinder and, at this time, the intake portpressure of the No. 4 cylinder is positive; referring to the range R ofthe crank angle of the No. 3 cylinder and the No. 4 cylinder, a vacuumis produced in the intake port of the No. 4 cylinder and, at this time,the intake port pressure of the No. 3 cylinder is positive; andreferring to the range S of the crank angle of the No. 1 cylinder andthe No. 3 cylinder, a vacuum is produced in the intake port of the No. 3cylinder and, at this time, the intake port pressure of the No. 1cylinder is positive. Consequently, referring to the No. 1 cylinder andthe No. 2 cylinder shown in FIG. 8, it will be understood that, in thefirst half of the intake stroke of the No. 1 cylinder, the mixture inthe intake port 5b of the No. 2 cylinder is fed into the intake port 5aof the No. 1 cylinder via the channel branch 30b, the common connectingchannel 29 and the channel branch 30a due to the pressure differencebetween the vacuum in the intake port 5a and the positive pressure inthe intake port 5b. In the same manner as described above, when the No.2 cylinder is in the intake stroke, the mixture in the intake port 5d ofthe No. 4 cylinder is fed into the intake port 5b of the No. 2 cylindervia the channel branch 30d, the common connecting channel 29 and thechannel branch 30b; when the No. 4 cylinder is in the intake stroke, themixture in the intake ports 5c of the No. 3 cylinder is fed into theintake port 5d of the No. 4 cylinder via the channel branch 30c, thecommon connecting channel 29 and the channel branch 30d; and when theNo. 3 cylinder is in the intake stroke, the mixture in the intake port5a of the No. 1 cylinder is fed into the intake port 5c of the No. 3cylinder via the channel branch 30a, the common connecting channel 29and the channel branch 30c. As mentioned above, due to the pressuredifference between the intake port pressures in the intake ports 5a, 5b,5c, 5d, the mixture is spouted from the channel.

FIG. 2 shows the case wherein the engine is operating under a lightload. Referring to FIG. 2, the throttle valve 22 is positioned at aposition illustrated in FIG. 2 and, therefore, at this time, a mixtureflow gap 33 is formed only between the lower edge of the throttle valve22 and the bottom wall of the branch mixture passage 18. Consequently,the flow velocity of the mixture formed in the carburetor body 13 isincreased as the mixture is collected towards the mixture flow gap 33.Then, the mixture passes through the mixture flow passage 33 at a highspeed. After this, the mixture flows only along the bottom wall of theintake port 5b at a high speed, as illustrated by the arrow A in FIG. 2,and then, flows into the combustion chamber 10 through the valve gapformed between the intake valve 3b and its valve seat. In addition, asmentioned previously, the mixture is spouted from the channel branch 30bat the time of the intake stroke. As is illustrated in FIG. 2, since theopening of the channel branch 30b is directed to the valve gap formedbetween the intake valve 3b and its valve seat, the velocity of themixture passing through the valve gap, as illustrated by the arrow A inFIG. 2, is increased by the mixture spouted from the channel branch 30band, as a result, the mixture is caused to flow into the combustionchamber 10 at an extremely high speed. At this time, since the intakeport 5b is tangentially connected to the circumferential inner wall ofthe combustion chamber 10, as illustrated in FIG. 2, a strong swirlmotion, shown by the arrow W in FIG. 1, is created in the combustionchamber 10 by the mixture flowing into the combustion chamber 10, asillustrated in FIG. 2. As a result of this swirl motion, a burningvelocity is considerably increased and a stable combustion can thus beobtained.

When the engine is operating under a heavy load, since the throttlevalve 22 is fully opened, as illustrated by the broken line in FIG. 2,the mixture flows in the intake port 5b through the entire cross-sectionthereof. However, at this time, since the mixture is spouted from thechannel branch 30b, a turbulence is created in the combustion chamber 10by the mixture spouted from the channel branch 30b even when the engineis operating under a heavy load.

FIG. 4 illustrates another embodiment according to the presentinvention. In this embodiment, a single variable venturi type carburetorbody 36 having a construction which is the same as that of thecarburetor body 13 illustrated in FIG. 2 is arranged in a carburetorhousing 35. The outlet passage of the carburetor body 36 is divided intotwo mixture passages 37, 38, and each of the mixture passages 37, 38 isdivided into four respective branch mixture passages 17, 18, 19, 20.Each of the throttle valves 21, 22, 23, 24 is arranged in the respectivebranch mixture passages 17, 18, 19, 20. In this embodiment, there is anadvantage in that the number of the carburetor bodies can be reduced ascompared with the case illustrated in FIG. 1.

FIGS. 5 through 7 illustrate a further embodiment according to thepresent invention. Referring to FIGS. 5 through 7 an intake manifold 40is fixed onto the engine body 1, and a carburetor 42 having a throttlevalve 41 is mounted on the intake manifold 40. The intake manifold 40comprises manifold branches 43, 44, 45, 46 which are connected to theintake ports 5a, 5b, 5c, 5d, respectively. Secondly throttle valves 47,48, 49, 50 are arranged in the outlets of the manifold branches 43, 44,45, 46, respectively, and attached onto a common valve shaft 51. As isillustrated in FIG. 5, an arm 53 attached onto a valve shaft 52 of thethrottle valve 41 is interconnected to an arm 54 attached onto thecommon valve shaft 51 by means of a link 55, so that the secondarythrottle valves 47, 48, 49, 50 are gradually opened as the throttlevalve 41 is gradually opened. In addition, as is illustrated in FIG. 5,a cross-section enlarged portion 44a is formed in the manifold branch44, and the secondary throttle valve 48 is arranged in the enlargedportion 44a. The upper wall 44b located at the end of the enlargedportion 44a forms a portion of a sphere, so that the mixture flow gap isnot formed between the upper wall 44b and the upper edge of thesecondary throttle valve 48 during the time the secondary throttle valve48 is rotated from the position illustrated by the solid line in FIG. 5to the position illustrated by the broken line in FIG. 5. Consequently,when the opening degree of the secondary throttle valve 48 is small and,thus, the engine is operating under a light load, the mixture flow gapis formed only between the lower edge of the secondary throttle valve 48and the bottom wall of the enlarged portion 44a and, as a result, themixture flows only along the bottom wall of the intake port 5b. Inaddition, as is illustrated in FIG. 3, it is preferable that a mixturestream guide plate 34 be arranged in the intake port 5b at a positionnear the bottom wall of the intake port 5b. By arranging the guide plate34 as mentioned above, the creation of the stream of the mixture flowingonly along the bottom wall of the intake port 5b can be ensured when theengine is operating under a light load. In this embodiment, the changesin pressure produced in the intake port at a position near the rear faceof the valve head of the intake valve are as shown in FIG. 8.Consequently, since the mixture is spouted from the channel branches30a, 30b, 30c, 30d into the combustion chamber 10 at a high speed, astrong swirl motion is created in the combustion chamber 10. Inaddition, in either of the above-described embodiments, it is possibleto recirculate the exhaust gas into the common connecting channel 29.

As is illustrated in FIGS. 1, 2, 4, 5, and 7, by positioning thethrottle valves 21, 22, 23, 24 at the outlets of the branch mixturepassages 17, 18, 19, 20 and by positioning the secondary throttle valves47, 48, 49, 50 at the outlets of the manifold branches 43, 44, 45, 46,the positive pressure which is caused by blowing the mixture back intothe intake port is maintained without being attenuated. As a result ofthis, since the pressure difference between the positive pressure andthe vacuum which act on the openings of the channel branches 30a, 30b,30c, 30d is maintained at a large pressure difference for a long time,it is possible to produce an extremely strong swirl motion in thecombustion chamber 10. In addition, since the mixture flows from theintake port of a given cylinder into the intake port of the othercylinder via the common connecting channel 29, the mixing operation ofthe mixture is improved and, at the same time, the distribution of fuelto each cylinder becomes uniform.

According to the present invention, by causing the mixture to flow onlyalong the bottom wall of the intake port and increasing the flowvelocity of that mixture by the mixture spouted from the channel branch,it is possible to produce a strong swirl motion in the combustionchamber when an engine is operating under a light load. As a result, theburning velocity can be increased independently of the engine speed whenan engine is operating under a light load while ensuring a highvolumetric efficiency when the engine is operating at a high speed undera heavy load.

While the invention has been described with reference to specificembodiments chosen for purposes of illustration, it should be apparentthat numerous modifications could be made thereto by those skilled inthe art without departing from the spirit and scope of the invention.

What is claimed is:
 1. A multi-cylinder internal combustion enginehaving a plurality of cylinders, each having a combustion chamber and anintake valve which has a valve head, said engine comprising:at least oneintake passage common to at least two cylinders and comprising acollecting portion having an inlet, and at least two branch intakepassages branched off from said collecting portion, each of said branchintake passages having an upper wall and a bottom wall and beingconnected to said respective combustion chamber via said correspondingintake valve; fuel supply means arranged in the inlet of said collectingportion; a common connecting passage; at least two branch connectingpassages each being connected to said common connecting passage andhaving an opening which opens into said respective branch intakepassages, and; at least two rotatable throttle valves each beingarranged in said respective branch intake passage at a position upstreamof the opening of said corresponding branch connecting passage andhaving an upper edge and a lower edge which cooperates with the bottomwall of said corresponding branch intake passage to form therebetween amixture flow passage, the cross sectional area of which is increased asthe corresponding throttle valve is rotated in accordance with anincrease in the level of the load of said engine, the upper edge of eachof said throttle valves cooperating with the upper wall of saidcorresponding branch intake passage to prevent a mixture from flowingbetween the upper edge of said corresponding throttle valve and theupper wall of said corresponding branch intake passage.
 2. Amulti-cylinder internal combustion engine as claimed in claim 1, whereineach of said throttle valves is attached onto a throttle shaft arrangedon the upper wall of said corresponding branch intake passage, the upperedge of each of said throttle valves cooperating with the upper wall ofsaid corresponding branch intake passage to always prevent the mixturefrom flowing between the upper edge of said corresponding throttle valveand the upper wall of said corresponding branch intake passage.
 3. Amulti-cylinder internal combustion engine as claimed in claim 2, whereinsaid throttle valves are attached onto a common throttle shaft.
 4. Amulti-cylinder internal combustion engine as claimed in claim 2, whereina wedge shaped groove is formed on the upper wall of each of said branchintake passages, said throttle shaft being arranged in said wedge shapedgroove.
 5. A multi-cylinder internal combustion engine as claimed inclaim 1, wherein each of said throttle valves is attached onto athrottle shaft extending through a center of said respective branchintake passage, the upper edge of each of said throttle valvescooperating with the upper wall of said corresponding branch intakepassage to prevent the mixture from flowing between the upper edge ofsaid corresponding throttle valve and the upper wall of saidcorresponding branch intake passage when the opening degree of each ofsaid throttle valves is below a predetermined degree.
 6. Amulti-cylinder internal combustion engine as claimed in claim 5, whereinsaid throttle valves are attached onto a common throttle shaft.
 7. Amulti-cylinder internal combustion engine as claimed in claim 5, whereineach of said branch intake passages comprises a reduced diameterportion, an increased diameter portion and a connecting portionconnecting said reduced diameter portion to said increased diameterportion, each of said throttle valves being arranged in saidcorresponding increased diameter portion and cooperating with the upperwall of said corresponding connecting portion at the upper edge of saidcorresponding throttle valve.
 8. A multi-cylinder internal combustionengine as claimed in claim 7, wherein the upper wall of said connectingportion forms a portion of a sphere.
 9. A multi-cylinder internalcombustion engine as claimed in claim 1, wherein each of said throttlevalves is arranged at a position near said intake valve.
 10. Amulti-cylinder internal combustion engine as claimed in claim 9, whereinsaid engine further comprises at least one carburetor housing formingtherein at least two mixture passages each having an outlet which isconnected to said respective combustion chamber via said correspondingintake valve, each of said throttle valves being arranged in said outletof said respective mixture passage.
 11. A multi-cylinder internalcombustion engine as claimed in claim 1, wherein said engine furthercomprises another throttle valve arranged in said intake passage, saidthrottle valves being operatively connected to said other throttle valvefor increasing the opening degree of said throttle valves in accordancewith an increase in the opening degree of said other throttle valve. 12.A multi-cylinder internal combustion engine as claimed in claim 11,wherein said throttle valves are mechanically connected to said otherthrottle valve by means of a link mechanism.
 13. A multi-cylinderinternal combustion engine as claimed in claim 11, wherein said enginefurther comprises at least one intake manifold having at least twooutlets, each of said throttle valves being arranged in the respectiveoutlet of said intake manifold.
 14. A multi-cylinder internal combustionengine as claimed in claim 1, wherein said engine further comprisesmixture guide means arranged in said branch intake passages at aposition located downstream of and near said throttle valves.
 15. Amulti-cylinder internal combustion engine as claimed in claim 14,wherein said mixture guide means comprises at least two guide plateseach being arranged in the vicinity of the bottom wall of saidrespective branch intake passage.
 16. A multi-cylinder internalcombustion engine as claimed in claim 1, wherein said common connectingpassage has a cross-section which is smaller than that of said branchintake passage.
 17. A multi-cylinder internal combustion engine asclaimed in claim 1, wherein each of said branch connecting passages hasa cross-section which is smaller than that of said branch intakepassage.
 18. A multi-cylinder internal combustion engine as claimed inclaim 1, wherein the opening of each of said branch connecting passagesis arranged in the vicinity of said valve head of said correspondingintake valve.
 19. A multi-cylinder internal combustion engine as claimedin claim 18, wherein the opening of each of said branch connectingpassages is directed to a valve gap formed between said correspondingintake valve and a valve seat thereof when said intake valve is opened.